<template>
  <scroll class="listview" 
          :data="data" 
          ref="listview" 
          :listenScroll="listenScroll"
          :probeType="probeType"
          @scroll="scroll">
    <ul>
      <li v-for="group in data" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li v-for="item in group.items" class="list-group-item" @click="selectItem(item)">
            <img class="avatar" v-lazy="item.avatar">
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
      <ul>
        <li v-for="(item,index) in shortcutList" 
            class="item" 
            :data-index="index"
            :class="{'current':currentIndex === index}">
          {{item}}
        </li>
      </ul>
    </div>
    <div class="list-fixed" ref="fixed">
      <div class="fixed-title">
        {{fixedTitle}}
      </div>
    </div>
    <div class="loading-container" v-show="!data.length">
      <loading></loading>
    </div>
  </scroll>
</template>

<script>
import Scroll from 'base/scroll/Scroll'
import {getData} from 'common/js/dom'
import Loading from 'base/loading/Loading'

const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT = 30

export default{
  props:{
    data:{
      type:Array,
      default:[]
    }
  },
  data(){
    return{
      scrollY:-1,
      currentIndex:0,
      diff:-1
    }
  },
  computed:{
    shortcutList(){
      return this.data.map(group=>{
        return group.title.substr(0,1)
      })
    },
    fixedTitle(){
      return this.data[this.currentIndex]?this.data[this.currentIndex].title:null
    }
  },
  //在props和data和computed里面都会自动生成一个get和set方法，会对两者里面的数据进行检测，用于与dom做绑定，而如果不需要进行数据检测的，就写在created里面
  created(){
      this.touch={}
      this.listenScroll = true
      this.listHeight = []
      this.probeType = 3
  },
  methods:{
    onShortcutTouchStart(e){
      let anchorIndex = getData(e.target,'index')
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
    },
    onShortcutTouchMove(e){
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = (this.touch.y2 - this.touch.y1)/ANCHOR_HEIGHT|0 //向下取整
      let anchorIndex = parseInt(this.touch.anchorIndex) + parseInt(delta)
      this._scrollTo(anchorIndex)
    },
    scroll(pos){
      this.scrollY = pos.y
    },
    selectItem(item){
      this.$emit('select',item)
    },
    _scrollTo(index){
      if(!index && index !== 0){
        return
      }
      if(index<0){
        index = 0
      }else if(index > this.listHeight.length -2){
        index = this.listHeight.length -2
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index],0) //后面一个0是滚动延迟时间
    },
    _calculateHeight(){
      this.listHeight = []
      const list = this.$refs.listGroup
      let height = 0
      this.listHeight.push(height)
      for(let i = 0; i< list.length; i++){
        let item = list[i]
        height+=item.clientHeight
        this.listHeight.push(height)
      }
    }
  },
  watch:{
    data(){
      setTimeout(()=>{
        this._calculateHeight()
      },20)
    },
    scrollY(newY){
      const listHeight = this.listHeight
      //当滚动到顶部，newY>0
      if(newY>0){
        this.currentIndex = 0
        return
      }
      //在中间部分滚动
      for(let i = 0; i < listHeight.length-1; i++){
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        if(-newY >= height1 && -newY < height2){
          this.currentIndex = i
          this.diff = height2 + newY
          return
        }
      }
      //在底部滚动,且-newY大于最后一个元素的上限
      this.currentIndex = listHeight.length - 2
    },
    diff(newVal){
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      if(this.fixedTop === fixedTop){
        return
      }
      this.fixedTop = fixedTop
      console.log(fixedTop)
      this.$refs.fixed.style.transform=`translate(0,${fixedTop}px)`
    }
  },
  components:{
    Scroll,
    Loading
  }
}
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"

  .listview
    position: relative
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>
